Processing math: 100%
J. Semicond. > 2015, Volume 36 > Issue 12 > 123001

SEMICONDUCTOR MATERIALS

Enhancement of phosphors-solubility in ZnO by thermal annealing

K. Mahmood1, N. Amin1, A. Ali1, M. Ajaz un Nabi1, M. Imran Arshad1, M. Zafar2 and M. Asghar2

+ Author Affiliations

 Corresponding author: K. Mahmood, Email: Khalid_mahmood856@yahoo.com

DOI: 10.1088/1674-4926/36/12/123001

PDF

Abstract: We have demonstrated the effect of annealing temperature on the diffusion density of phosphors in zinc oxide. The P-dopant P430 was sprayed on ZnO pellets and annealed at different temperatures from 500 to 1000℃ with a step of 100℃ for one hour using a programmable furnace. The concentration of P was controlled by varying the annealing temperature and the maximum solubility of P(3% At) was achieved at annealing 800℃ determined by energy dispersive X-ray diffraction(EDX) measurements. X-ray diffraction(XRD) confirmed the hexagonal structure of ZnO and showed that the growth direction was along the c-axis. We observed a maximum up shift in the(002) plane at an annealing temperature of 800℃, suggesting that P atoms replaced Zn atoms in the structure which results in the reduction of the lattice constant. Room temperature photoluminescence(PL) spectrum consists of a peak at 3.28 eV and related to band edge emission, but samples annealed at 800 and 900℃ have an additional donor acceptor pair peak at 3.2 eV. Hall effect measurements confirmed the p-type conductivity of the sample annealed at 800℃.

Key words: ZnOP-dopantEDXXRDPL

Zinc oxide is a very important material for electronic and optoelectronic devices because of its excellent properties of direct and wide band gap and large exciton binding energy[1, 2]. The greatest challenge for these applications,however,remains the fabrication of reliable and stable p-type ZnO with low resistivity and high carrier concentration[3]. This p-type doping issue is related to the formation and compensation effects of native donor defects such as O vacancies and Zn interstitials,low solubility of p-dopants and higher activation energy of acceptors in the band gap of ZnO[4, 5, 6]. It is reported in the literature that even nitrogen and phosphorous are the most favorable p-type dopants in ZnO,but stable p-type conductivity is hard to achieve due to the low solubility[7]. The solubility limit for acceptor impurities in ZnO,as well as other wide-gap materials suffering from doping asymmetry,can be enhanced above the thermodynamic limit by employing ``non-equilibrium'' conditions. One way to improve the dopant solubility is through adjusting dopant chemical potential μA. The chemical potential of an acceptor dopant in the ZnO matrix determines the dopant solubility[8]. Therefore,raising this potential would increase the solubility of the dopant coupled with avoidance of precipitate formation. High temperature annealing is a very efficient way to facilitate the enhancement of P concentration. Furthermore,high temperature annealing can activate the P atoms in ZnO,suppress the formation of PO defects and reduce the density of oxygen vacancies[9]. Therefore,a high temperature annealing study would be very helpful to grow stable p-type ZnO.

In this paper,we have achieved high solubility of phosphorous in bulk ZnO by using high temperature annealing conditions. The ZnO pellets were annealed from 500 to 1000 ℃ in a programmable furnace; it was found that the maximum concentration of P occurred in a sample annealed at 800 ℃. The results were explained with the help of XRD,PL and Hall measurements.

ZnO pellets were synthesized by the conventional sintering technique in an atmospheric furnace using a zinc oxide powder (99.99%). The ZnO powders were first milled in an agate mortar and heated in air at an annealing temperature of 300 ℃ for 2 h to evaporate the water and remove the organic residuals. The obtained powders were then pressed into pellet discs (of about 1 mm in thickness and 8 mm in diameter). A drop of phosphors dopant P430 was sprayed on the surface of pellets and then subjected to the annealing process. The pellets annealed at different temperatures from 500 to 1000 ℃,keeping a step of 100 ℃ using a programmable furnace for one hour.

The characterization of annealed samples was done by using following equipments; SEM/EDX (3000 Hitachi),PL/Raman (Photon Systems) having laser wavelength 248 nm,Hall effect by Ecopia 3000 and XRD (miniflex Rigaku). All the measurements were performed at room temperature.

Figure1 shows the EDX results of P-doped ZnO annealed at different temperatures from 500 to 1000 ℃. The figure shows that the concentration of phosphorous increases with annealing temperature up to an annealing temperature of 800 ℃ and again decreases for samples annealed at higher temperatures. Moreover,the concentration of oxygen content in the samples also increases with annealing temperature. The O-rich growth conditions suppress the formation of PO acceptor defects and instead increase the probability of generating Zn vacancies and O-interstitials due to the Zn deficiency conditions. Among them,Zn vacancy-related defects result in the rapid incorporation of P atoms in the Zn sites,and the ultimate result is the formation of a PZn-2VZn acceptor complex[10]. The formation mechanism of this acceptor complex has already been reported by many authors[11, 12]. To verify the p-type conductivity of annealed samples,we have performed Seebeck measurements. The results suggested that samples annealed at 800 and 900 ℃ showed p-type conductivity and the rest all showed n-type conductivity. This result confirmed that the maximum diffusion of P atoms into ZnO pellets occurred at an annealing temperature of 800 ℃.

Figure  1.  EDX measurements of bulk ZnO annealed at different temperatures from 500 to 1000 ℃.

Typical XRD patterns of the P-doped ZnO pellets sintered at different temperatures (500 to 1000 ℃ with a step of 100 ℃) for one hour demonstrated `2θ values' of 8 diffraction peaks corresponding to the ZnO (100),(002),(101),(102),(110),(103),(200) and (112) planes,respectively. A comparison with the JCPD 36-1451 Card confirmed the formation of hexagonal zinc oxide[13, 14]. For clarity,we have displayed only the dominant diffraction peaks corresponding to the (002) plane,in Figure2. We clearly see that the 2θ value of the major peak of the representative ZnO samples varies with the sintering temperature. The 2θ value of the peak increases and reaches 34.6 at the annealing temperature of 800 ℃ shown in the inset of Figure2. According to the size consideration of P,an increase in lattice constant is expected when a P atom occupies an O site (smaller in size than P); otherwise,the lattice constant should decrease when a P atom occupies a Zn site (larger in size than P)[15]. Practically,the (002) plane of the ZnO shifts towards a higher 2θ value with the sintering temperatures up to 800 ℃ and thus yields a smaller lattice constant. Henceforth,we will refer the filling of Zn site with P as an A-type shift. Accordingly,the information from the literature suggest that a P atom while occupying a Zn site may generate two Zn vacancies and hence produces a shallow acceptor PZn-2VZn complex above the valence band maximum.

Figure  2.  (Color online) X-ray diffraction pattern of P-doped bulk ZnO annealed from 500 to 1000 ℃. Inset demonstrated the effect of annealing temperature on the peak position of ZnO (002) plane.

The room temperature PL measurements were carried out to examine the effect of annealing on the optical properties of the P-doped ZnO pellets. Figure3 compares the photoluminescence spectra of doped samples measured at room temperature. All samples consist of a band to band emission at 3.29 eV,but samples annealed at 800,900 and 1000 ℃ have an additional peak at 3.2 eV[16]. This additional peak is related with the donor acceptor pair,where the acceptor is the P atom.

Figure  3.  (Color online) Photoluminescence spectra of P-doped ZnO powder annealed at 500-1100 ℃.

The Hall measurements were performed to calculate the carrier concentration of P-doped samples and shown in Figure4. The graph shows that the hole concentration is maximum for a sample annealed at 800 ℃. The observed result can be explained as follows: as the annealing temperature increases the P doping increases,which formed an acceptor complex level with VZn,therefore the carrier concentration increases. All other samples show the n-type conductivity (not shown here).

Figure  4.  Annealing temperature versus carrier concentration graph.

In conclusion,we have successfully enhanced the phosphorous diffusion in ZnO pellets to achieve p-type conductivity. ZnO pellets were doped with P using high temperature annealing conditions. The maximum diffusion of P atoms occurred at the annealing temperature of 800 ℃,confirmed by EDX measurements. The shifting of the (002) ZnO plane towards higher 2θ angles in XRD and emerging of donor acceptor pair in PL spectra at the annealing temperature of 800~℃ strongly suggested that maximum diffusion of P atoms occurred at the annealing temperature of 800 ℃.

Authors are thankful to the Higher Education Commission (HEC) of Pakistan for the financial assistance under project # IPFP/HRD/HEC/2014/2016.



[1]
[2]
[3]
[4]
[5]
[6]
[7]
[8]
[9]
[10]
[11]
[12]
[13]
[14]
[15]
[16]
Fig. 1.  EDX measurements of bulk ZnO annealed at different temperatures from 500 to 1000 ℃.

Fig. 2.  (Color online) X-ray diffraction pattern of P-doped bulk ZnO annealed from 500 to 1000 ℃. Inset demonstrated the effect of annealing temperature on the peak position of ZnO (002) plane.

Fig. 3.  (Color online) Photoluminescence spectra of P-doped ZnO powder annealed at 500-1100 ℃.

Fig. 4.  Annealing temperature versus carrier concentration graph.

[1]
[2]
[3]
[4]
[5]
[6]
[7]
[8]
[9]
[10]
[11]
[12]
[13]
[14]
[15]
[16]
1

Phase transformation from cubic ZnS to hexagonal ZnO by thermal annealing

K. Mahmood, M. Asghar, N. Amin, Adnan Ali

Journal of Semiconductors, 2015, 36(3): 033001. doi: 10.1088/1674-4926/36/3/033001

2

Effect of ZnO films on CdTe solar cells

Liu Tingliang, He Xulin, Zhang Jingquan, Feng Lianghuan, Wu Lili, et al.

Journal of Semiconductors, 2012, 33(9): 093003. doi: 10.1088/1674-4926/33/9/093003

3

Optical and electrical properties of N-doped ZnO and fabrication of thin-film transistors

Zhu Xiaming, Wu Huizhen, Wang Shuangjiang, Zhang Yingying, Cai Chunfeng, et al.

Journal of Semiconductors, 2009, 30(3): 033001. doi: 10.1088/1674-4926/30/3/033001

4

Influence of Be-Doping on Electronic Structure and Optical Properties of ZnO

Zheng Yongping, Chen Zhigao, Lu Yu, Wu Qingyun, Weng Zhenzhen, et al.

Journal of Semiconductors, 2008, 29(12): 2316-2321.

5

Influence of the Annealing Temperature on the Structural and Optical Properties of N-Doped ZnO Films

Zhong Sheng, Xu Xiaoqiu, Sun Lijie, Lin Bixia, Fu Zhuxi, et al.

Journal of Semiconductors, 2008, 29(7): 1330-1333.

6

Defects and Properties of Antimony-Doped ZnO Single Crystal

Zhang Rui, Zhang Fan, Zhao Youwen, Dong Zhiyuan, Yang Jun, et al.

Journal of Semiconductors, 2008, 29(10): 1988-1991.

7

Effect of Hydrogenation on Luminescence Properties of ZnO Crystals

Zhang Yuantao, Ma Yan, Zhang Baolin, Du Guotong

Journal of Semiconductors, 2008, 29(3): 526-529.

8

Preparation and Acetone Sensing Properties of Flower-Like ZnO Nanorods

Liu Li, Feng Yingliang, Yu Lianxiang, Wang Lianyuan, Zhang Tong, et al.

Journal of Semiconductors, 2008, 29(12): 2372-2375.

9

Effects of Growth Parameters on Proprties of P-Type ZnO Films Grown by MOCVD

Lu Yangfan, Ye Zhizhen, Zeng Yujia, Xu Weizhong, Zhu Liping, et al.

Chinese Journal of Semiconductors , 2007, 28(S1): 275-278.

10

Single Crystalline Co-Doped ZnO Thin Films by Molecular Beam Epitaxy and Room Temperature Ferromagnetism

Cao Qiang, Liu Guolei, Deng Jiangxia, Xing Pengfei, Tian Yufeng, et al.

Chinese Journal of Semiconductors , 2007, 28(S1): 282-284.

11

Low Temperature Synthesis and Optical Properties of ZnO Nanowires

Chang Peng, Liu Su, Chen Rongbo, Tang Ying, Han Genliang, et al.

Chinese Journal of Semiconductors , 2007, 28(10): 1503-1507.

12

Fabrication and Magnetic Property of Mn Doped ZnO Nanowires

Chang Yongqin, Yu Dapeng, Long Yi

Chinese Journal of Semiconductors , 2007, 28(S1): 296-299.

13

Simulation of the ZnO-MOCVD Horizontal Reactor Geometry

Liu Songmin, Gu Shulin, Zhu Shunming, Ye Jiandong, Liu Wei, et al.

Chinese Journal of Semiconductors , 2007, 28(S1): 309-311.

14

Effect of Different Facets of on the Growth of vapor deposition

Zhang Panfeng, Wei Hongyuan, Fan Haibo, Cong Guangwei, Yang Shaoyan, et al.

Chinese Journal of Semiconductors , 2007, 28(S1): 289-292.

15

First-Principles Calculation of ZnO Doped with Ag

Wan Qixin, Xiong Zhihua, Rao Jianping, Dai Jiangnan, Le Shuping, et al.

Chinese Journal of Semiconductors , 2007, 28(5): 696-700.

16

Optical and Electrical Properties of ZnO/PS Heterostructure

Zhao Bo, Li Qingshan, Zhang Ning, Chen Da, Zheng Xuegang, et al.

Chinese Journal of Semiconductors , 2006, 27(7): 1217-1220.

17

Fabrication of ZnO Nanowires by Vapor-Phase Deposition and Their Field Emission Properties

Zhang Qifeng, Rong Yi, 陈贤祥, Chen Xianxiang, 张兆祥, et al.

Chinese Journal of Semiconductors , 2006, 27(7): 1225-1229.

18

Effect of Growth Temperature on Properties of ZnO Thin Films

Su Hongbo, Dai Jiangnan, Pu Yong, Wang Li, Li Fan, et al.

Chinese Journal of Semiconductors , 2006, 27(7): 1221-1224.

19

Solution Growth of Morphology Controllable ZnO One-Dimensional Nanorods and Microrods

Zhang Linli, Guo Changxin, Chen Jiangang, Hu Juntao

Chinese Journal of Semiconductors , 2005, 26(11): 2127-2132.

20

Fabrication of ZnO Light-Emitting Diode by Using MOCVD Method

Ye Zhizhen, Xu Weizhong, Zeng Yujia, Jiang Liu, Zhao Binghui, et al.

Chinese Journal of Semiconductors , 2005, 26(11): 2264-2266.

1. Mondal, S., Basak, D. Photophysical investigation of the formation of defect levels in P doped ZnO thin films. Ceramics International, 2022. doi:10.1016/j.ceramint.2022.03.275
2. Faraz, A., Mahmood, K., Ali, A. et al. Enhancement of Al-N co-dopant solubility in ZnO by high temperature thermal annealing. Ceramics International, 2019, 45(3): 2948-2952. doi:10.1016/j.ceramint.2018.10.005
3. Boukhenoufa, N., Mahamdi, R., Rechem, D. Structural, optical, morphological and electrical properties of undoped and Al-doped ZnO thin films prepared using sol-gel dip coating process. Journal of Semiconductors, 2016, 37(11): 113001. doi:10.1088/1674-4926/37/11/113001
  • Search

    Advanced Search >>

    GET CITATION

    K. Mahmood, N. Amin, A. Ali, M. Ajaz un Nabi, M. Imran Arshad, M. Zafar, M. Asghar. Enhancement of phosphors-solubility in ZnO by thermal annealing[J]. Journal of Semiconductors, 2015, 36(12): 123001. doi: 10.1088/1674-4926/36/12/123001
    K. Mahmood, N. Amin, A. Ali, M. Ajaz un Nabi, M. Imran Arshad, M. Zafar, M. Asghar. Enhancement of phosphors-solubility in ZnO by thermal annealing[J]. J. Semicond., 2015, 36(12): 123001. doi: 10.1088/1674-4926/36/12/123001.
    shu

    Export: BibTex EndNote

    Article Metrics

    Article views: 2579 Times PDF downloads: 16 Times Cited by: 3 Times

    History

    Received: 08 April 2015 Revised: Online: Published: 01 December 2015

    Catalog

      Email This Article

      User name:
      Email:*请输入正确邮箱
      Code:*验证码错误
      K. Mahmood, N. Amin, A. Ali, M. Ajaz un Nabi, M. Imran Arshad, M. Zafar, M. Asghar. Enhancement of phosphors-solubility in ZnO by thermal annealing[J]. Journal of Semiconductors, 2015, 36(12): 123001. doi: 10.1088/1674-4926/36/12/123001 ****K. Mahmood, N. Amin, A. Ali, M. Ajaz un Nabi, M. Imran Arshad, M. Zafar, M. Asghar. Enhancement of phosphors-solubility in ZnO by thermal annealing[J]. J. Semicond., 2015, 36(12): 123001. doi: 10.1088/1674-4926/36/12/123001.
      Citation:
      K. Mahmood, N. Amin, A. Ali, M. Ajaz un Nabi, M. Imran Arshad, M. Zafar, M. Asghar. Enhancement of phosphors-solubility in ZnO by thermal annealing[J]. Journal of Semiconductors, 2015, 36(12): 123001. doi: 10.1088/1674-4926/36/12/123001 ****
      K. Mahmood, N. Amin, A. Ali, M. Ajaz un Nabi, M. Imran Arshad, M. Zafar, M. Asghar. Enhancement of phosphors-solubility in ZnO by thermal annealing[J]. J. Semicond., 2015, 36(12): 123001. doi: 10.1088/1674-4926/36/12/123001.

      Enhancement of phosphors-solubility in ZnO by thermal annealing

      DOI: 10.1088/1674-4926/36/12/123001
      More Information
      • Corresponding author: Email: Khalid_mahmood856@yahoo.com
      • Received Date: 2015-04-08
      • Accepted Date: 2015-06-12
      • Published Date: 2015-01-25

      Catalog

        /

        DownLoad:  Full-Size Img  PowerPoint
        Return
        Return